Arc lamp having an acoustical mode absorber

ABSTRACT

A high-intensity arc lamp is disclosed. The arc lamp includes an arc chamber having an optical reflector at one end and an optical window at the other end and an anode and a cathode electrode disposed within the chamber in spaced relation to define an arc therebetween. A housing is coupled to the arc chamber via a gas passageway. The housing includes a mode-absorbing structure, such as a mass of intertwined refractory fibers, a stack of baffle plates, or a stack of tuned grid wires, which are acoustically coupled to the arc chamber for coupling to the resonant acoustical modes thereof for suppression of such modes to improve the stability of the arc.

United States Patent John F. Richter Mountain View, Calii. 839,499

July 7, 1969 Jan. 4, 1972 Varian Associates Palo Alto, Calif.

[72] Inventor [21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] ARC LAMP HAVING AN ACOUSTICAL MODE Primary ExaminerDavid Schonberg Assistant ExaminerPaul A. Sacher Attorneys-Stanley Z. Cole and Gerald L. Moore AESTRACT: A high-intensity arc lamp is disclosed. The are lamp includes an arc chamber having an optical reflector at one end and an optical window at the other end and an anode and a cathode electrode disposed within the chamber in spaced relation to define an arc therebetween. A housing is coupled to the arc chamber via a gas passageway. The housing includes a mode-absorbing structure, such as a mass of intertwined refractory fibers, a stack of baffle plates, or a stack of tuned grid wires, which are acoustically coupled to the arc chamber for coupling to the resonant acoustical modes thereof for suppression of such modes to improve the stability of the arc.

PATENTED-Ml w: alsssLoso FIGI 7 INVENTOR. T

JOHN F. RICHTER BY ATTORNEY ARC LAMP HAVING AN ACOUSTICAL MODE ABSORBER DESCRIPTION OF THE PRIOR ART Heretofore, high intensity are lamps have been built wherein anode and cathode electrodes were spaced apart to define an arc gap within a chamber having a reflector at one end and an optical window at the other. Such arc lamps have been filled with an ionizable gas, such as xenon at approximately 25 atmospheres. Such a high intensity are lamp is disclosed and claimed in copending US. application Ser. No. 655,717, filed July 14, I967 now Pat. No. 3,502,929 and assigned to the same assignee as the present invention.

One of the problems encountered in these prior art high intensity arc lamps is that are chamber is capable of supporting certain acoustically resonant modes. These modes can be excited by electrical modulation of the are or by mechanical resonances of certain of the elements of the lamp. Excitation of the acoustical resonant modes within the arc chamber produce pressure waves which cause arc instability or can actually snuff out the arc, which requires restarting of the lamp. This are instability is particularly troublesome when the light intensity is modulated by electrically modulating the arc. In a typical prior art lamp, the arc was quite often extinguished when the modulation frequency reached the range above 8 kilohertz.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved high-intensity arc lamp.

One feature of the present invention is the provision of a mode suppression means acoustically coupled to the interfering acoustical resonant modes existing within the arc chamber for suppressing resonance of the interfering acoustical modes to improve the stability of the arc.

Another feature of the present invention is the same as the preceding feature wherein the mode suppression means includes a mass of intertwined refractory fibers disposed in a housing in gas communication with a gas fill of the arc chamber for absorbing acoustical energy from. the interfering resonant modes to reduce their Q.

Another feature of the present invention is the same as the first feature wherein the acoustical mode suppression means includes a stack of space-apart baffle plates disposed in a housing in gas communication with the gas fill of the arc chamber for baffling the acoustical wave energy of the interfering resonant modes therein.

Another feature of the present invention is the same as the first feature wherein the acoustical mode suppression means includes a stack of spaced-apart grid structures, each grid structure including a plurality of wires supported at their ends in tension and turned for different resonant frequencies within the band of frequencies of the interfering acoustical resonant modes for absorbing energy therefrom and lowering their 0.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a longitudinal sectional view of an arc lamp incorporating features of the present invention,

FIG. 2 is a view of the structure of FIG. I taken along line 2-2 in the direction of the arrows,

FIG. 3 is an enlarged detail view of a portion of the structure of FIG. 3 delineated by line 3-3 and depicting an alternative mode suppression structure,

FIG. 4 is a view similar to that of FIG. 3 depicting an alternative mode suppression structure,

FIG. 5 is a view of the structure of FIG. 4 taken along line 5-5 in the direction of the arrows,

FIG. 6 is a longitudinal sectional view of an arc lamp depicting an alternative mode suppression structure of the present invention, and

FIG. 7 is a schematic circuit diagram, partly in block diagram form, of an electrical circuit for energizing the arc lamp of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2 there is shown a high-intensity arc lamp I incorporating features of the present invention. The lamp 1 includes a high-intensity arc chamber 2 having a concave optical reflector 3 as of nickel clad Kovar disposed at one end and an optically transparent window 41, as of sapphire, disposed at the other end facing the concave surface of the reflector 3. The reflector 3 includes an outwardly flanged portion 5 which is sealed in a gastight manner to an annular ceramic insulator ring 6, as of alumina. The other end of the alumina insulator 6 is brazed to a terminal ring 7, as of lKovar, which in turn is brazed to a flange portion of a window frame 8, as of Kovar, having the disk-shaped window member 4 brazed thereacross. In a typical example, the inside dimensions of the arc chamber 2 are approximately I inch diameter and 1.25 inches in axial length.

Anode and cathode electrodes, 9 and II, respectively, are axially disposed of the arc chamber 2 in spaced relation to define an arc gap 12, as of approximately 1 mm. in length, between the mutually opposed ends of the anode and cathode electrodes. In a typical example the anode electrode 9 is made of tungsten and the cathode electrode II is made of thoriated tungsten.

The anode electrode 9 is carried from terminal ring 7 via a plurality of support legs 13, as of molybdenum. Support legs 13 are brazed at their outer ends to the "terminal ring 7 and are curved to accommodate thermal expansion and contraction of the support legs in use.

The cathode electrode Ill projects into the arc chamber 2 through a central aperture I4 in the reflector 3. An ancillary cup-shaped housing member 15 surrounds the cathode electrode II and is brazed thereto at the marginal lip of a central aperture 16 in the bottom wall of the cup I5. The lip of the cup 15 is brazed to the outer surface of the reflector 3.

The are chamber 2 is filled with an ionizable gas such as xenon to a relatively high pressure as of 25 atmospheres. Other suitable gas fills include argon and krypton.

Referring now to FIG. 7, there is shown an electrical circuit for energizing the lamp I. A power supply 18 supplies a relatively low voltage as of 10 volts with a relatively high current capacity as of 10 amps across terminals 7 and 11 of the lamp I via leads I9 and 20. Lead 20 is grounded, whereas lead I9 includes a series connection of the secondary windings 22 and 23 of a pair of transformers 24 and 25, respectively. The primary winding 26 of transformer 24 is connected to the output of a power modulator 27 for amplitude or pulse modulating the power supplied to the lamp I. Transformer 25 is a high voltage stepup transformer and the primary winding 28 thereof is connected to the output of a starter 29 which supplies a short spike of voltage to the primary which is stepped up via stepup transformer 25 to a relatively high voltage as of 3,000 volts to be applied across the electrodes of the lamp 1 to initiate the arc therein. Once the arc is initiated, the current is modulated via modulator 27 to permit information to be put upon the output light beam from the lamp I.

It has been found that the arc chamber 2 forms an acoustical resonator capable of supporting acoustical resonant modes. For a lamp of the aforecited dimensions it has been found that these acoustical modes of resonance have resonant frequencies in the range of 8 to 9 kilohertz and when excited as by electrical modulation of the are via modulator 27 these resonant acoustical modes result in instability and possible extinction of the arc. However, it has been found that these resonant modes can be substantially suppressed by inserting a mode suppression means within the ancillary housing I5 which is in gas communication with the arc chamber 2 via aperture 14. More particularly, in one embodiment of the present invention, the ancillary housing I5 is filled with a mass of intertwined refractory fibers, as of tungsten, quartz, or mixtures thereof. By loading the ancillary chamber 15 with the intertwined fibers the resonant interfering acoustical modes are heavily damped, thereby lowering their Q and preventing instabilities in the arc up to modulation frequencies of l2 kilohertz.

Referring now to FIG. 3, there is shown an alternative mode suppression means disposed within the ancillary housing 15. In this embodiment the mode suppression means comprises a stack of centrally apertured relatively shallow cup-shaped baffle members 31 as of 0.002 inches thick nickel brazed to the inside wall of the cup-shaped housing 15. Cup-shaped members 31 are centrally apertured to permit passage of the cathode electrode 11 axially therethrough and to provide an annular coupling space between the cups and the cathode electrode 11 which permits gas communication between the successive cups 31 and between the cups and the arc chamber 2 via the central aperture 14 in the reflector 3. The baffle cups 31 serve to baffle the pressure waves of the resonant modes within the arc chamber, thereby absorbing the energy from these resonant interfering modes and lowering their Q to prevent interference with the arc. In a typical example, 7 baffle cups 31 were employed and they served to stabilize the arc to modulation frequencies above I l kilohertz.

Referring now to FIGS. 4 and 5, there is shown an altemative mode suppression means disposed within the ancillary housing 15. In this embodiment the mode suppression means include a stack of grid structures 32. Each grid structure includes an annular frame member 33, as of tungsten, having a plurality of grid wires 34, as of tungsten, supported in tension at their ends from the frame 33. The grid wires are dimensioned and tensioned to be resonant within the band of frequencies of the interfering acoustical resonant modes and harmonics thereof. The resonant grid wires couple to the resonant acoustical modes within the arc chamber 2 and serve to absorb energy from these resonant modes lowering their Q to prevent instabilities in the arc.

Referring now to FIG. 6, there is shown an alternative embodiment of the present invention. In this embodiment, the lamp 37 is similar to that of FIG. 1 with the exception that the anode 9 is supported from an annular window frame number 38 via support legs 13. The annular window frame number 38 is a a generally U-shaped channel cross section with the window 4 being sealed across the inside diameter of the annular frame member 38. The outer leg of the channel frame number 38 is sealed as by heliarc welding at 39 to the flanged lip of the reflector 3. An annular gas passageway 41 is defined by a gap between the inside leg of the channel-shaped frame member 38 and the lip of the reflector 3. The annular gas passageway 41 communicates with the annular region defined within the interior of the channel frame member 38 which also defines an ancillary annular housing 42. The annular housing 42 is filled with intertwined refractory fibers as of tungsten, quartz, or mixtures thereof. As in the embodiment of FIG. 1, the intertwined fibers in gas communication with the arc chamber 2 serve to couple to interfering resonant acoustical modes of the arc chamber 2 for loading these modes and lowering their such that they do not cause instabilities in the arc.

The cathode electrode 11 is supported from the reflector 3 by a cup-shaped frame member 43, insulator ring 44 and an adapter frame member 45 sealed between the insulator ring 44 and the reflector 3. Cathode electrode 11 is brazed to the lip of a central aperture in the bottom of the cup-shaped frame member 43.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Iclaim:

I. In an arc lamp, means defining a chamber bounded by an optical reflector and an optical window op osed to said reflector, means forming cathode and anode e ectrodes extending into said chamber in spaced relation to define an arc gap therebetween said chamber being filled with an ionizable gas for supporting an arc across said arc gap, said chamber being capable of supporting interfering acoustical resonant modes in the form of acoustical waves propagating through said ionizable gas and thereby causing instability of the arc, THE IM- PROVEMENT COMPRISING, acoustical mode suppression means located within an ancillary housing in gas communication with said chamber and acoustically coupled to the interfering acoustical resonant modes for suppressing resonance thereof to improve the stability of the arc.

2. The apparatus of claim 1 wherein said acoustical mode suppression means includes a mass of intertwined refractory fibers disposed in gas communication with the gas fill of said chamber for absorbing acoustical energy from the interfering resonant modes to reduce their Q.

3. The apparatus of claim 1 wherein said acoustical mode suppression means includes a stack of spaced-apart baffle plates disposed in gas communication with the gas fill of said chamber for baffling the acoustical wave energy of the interfering resonant modes coupled to said stack of baffle plates.

4. The apparatus of claim 1 wherein said acoustical mode suppression means includes a stack of spaced-apart grid structures, each grid structure including a plurality of wires supported at their ends in tension, said tensioned wires being tuned for different resonant frequencies within the band of frequencies of the interfering acoustical resonances for absorbing energy therefrom and lowering their Q.

5. The apparatus of claim 1 wherein said optical reflector has a concave face disposed facing said window, said reflector including a central aperture for passage of one of said electrodes therethrough, a housing enclosing said one electrode and communicating with said chamber via said central aperture in said reflector, and wherein said acoustical mode suppression means is disposed in said housing.

6. The apparatus of claim 5 wherein said mode suppression means includes a mass of intertwined refractory fibers disposed in said housing.

7. The apparatus of claim 6 wherein said fibers are selected from the group consisting of tungsten, quartz, and mixtures thereof.

8. The apparatus of claim 5 wherein said mode suppression means includes a stack of spaced-apart baffle plates disposed in said housing.

9. The apparatus of claim 5 wherein said mode suppression means includes a stack of grids disposed in said housing.

10. The apparatus of claim 1 including a housing disposed external to said chamber, means forming a gas passageway communicating between said housing and said chamber, and wherein said mode suppression means includes a mass of intertwined fibers disposed in said housing for absorbing acoustical energy from the interfering resonant acoustical modes coupled to said housing via said gas passageway. 

1. In an arc lamp, means defining a chamber bounded by an optical reflector and an optical window opposed to said reflector, means forming cathode and anode electrodes extending into said chamber in spaced relation to define an arc gap therebetween, said chamber being filled with an ionizable gas for supporting an arc across said arc gap, said chamber being capable of supporting interfering acoustical resonant modes in the form of acoustical waves propagating through said ionizable gas and thereby causing instability of the arc, THE IMPROVEMENT COMPRISING, acoustical mode suppression means located within an ancillary housing in gas communication with said chamber and acoustically coupled to the interfering acoustical resonant modes for suppressing resonance thereof to improve the stability of the arc.
 2. The apparatus of claim 1 wherein said acoustical mode suppression means includes a mass of intertwined refractory fibers disposed in gas communication with the gas fill of said chamber for absorbing acoustical energy from the interfering resonant modes to reduce their Q.
 3. The apparatus of claim 1 wherein said acoustical mode suppression means includes a stack of spaced-apart baffle plates disposed in gas communication with the gas fill of said chamber for baffling the acoustical wave energy of the interfering resonant modes coupled to said stack of baffle plates.
 4. The apparatus of claim 1 wherein said acoustical mode suppression means includes a stack of spaced-apart grid structures, each grid structure including a plurality of wires supported at their ends in tension, said tensioned wires being tuned for different resonant frequencies within the band of frequencies of the interfering acoustical resonances for absorbing energy therefrom and lowering their Q.
 5. The apparatus of claim 1 wherein said optical reflector has a concave face disposed facing said window, said reflector including a central aperture for passage of one of said electrodes therethrough, a housing enclosing said one electrode and communicating with said chamber via said central aperture in said reflector, and wherein said acoustical mode suppression means is disposed in said housing.
 6. The apparatus of claim 5 wherein said mode suppression means includes a mass of intertwined refractory fibers disposed in said housing.
 7. The apparatus of claim 6 wherein said fibers are selected from the group consisting of tungsten, quartz, and mixtures thereof.
 8. The apparatus of claim 5 wherein said mode suppression means includes A stack of spaced-apart baffle plates disposed in said housing.
 9. The apparatus of claim 5 wherein said mode suppression means includes a stack of grids disposed in said housing.
 10. The apparatus of claim 1 including a housing disposed external to said chamber, means forming a gas passageway communicating between said housing and said chamber, and wherein said mode suppression means includes a mass of intertwined fibers disposed in said housing for absorbing acoustical energy from the interfering resonant acoustical modes coupled to said housing via said gas passageway. 